The invention herein described relates generally to a method for forming a porous insulating article (or composition or compound), and more specifically to the compounds used in the process to make the same.
As a consequence of the progress made in integrated circuit technology, the spacing between the metal lines on any given plane of an integrated circuit has become less and less, now extending into the submicrometer range. By reducing the spacing between conductive members in the integrated circuit, an increase in capacitive coupling occurs. This increase in capacitive coupling causes greater crosstalk, higher capacitive losses and increased resistor capacitor (RC) time constant.
Inorganic materials such as silicon dioxide and silicon nitride have been traditionally used in the microelectronics industry as insulating and passivating materials in the manufacture of integrated circuits. However, as the demand for smaller, faster, and more powerful devices becomes prevalent new materials will be needed to enhance the performance and the efficient manufacture of these devices.
To meet these enhanced performance and manufacturing criteria, considerable interest in high performance polymers characterized by low dielectric constant, low moisture uptake, good substrate adhesion, chemical resistance, high glass transition temperatures (e.g., Tg greater than 250xc2x0 C.), toughness, high thermal and thermal-oxidative stabilities, as well as good optical properties are increasingly gaining momentum. Such polymers are useful as dielectric coatings and films in the construction and manufacture of multichip modules (MCMs) and in integrated circuits (IC), in electronic packaging, in flexible film substrates, and in optical applications such as in flat panel displays and the like.
In order to reduce capacitive coupling, much effort has been directed toward developing low dielectric constant (low-K) materials to replace conventional dielectric materials that are interposed between the metal lines on a given layer and between layers. Many conventional electronic insulators have dielectric constants (∈) in the 3.5 to 4.2 range. For example, silicon dioxide has a dielectric constant of 4.2 and polyimides typically have dielectric constants from 2.9 to 3.5. Alternatively, the silicon dioxide can be decreased by adding fluorine in place of oxygen to yield a substance with a dielectric constant of approximately 3.5. Some advanced polymers have dielectric constants in the 2.5 to 3.0 range. Materials in the 1.8 to 2.5 range are also known, but such materials have had associated therewith severe processing, cost and materials problems.
The lowest possible, or ideal, dielectric constant is 1.0, which is the dielectric constant of a vacuum. Air is almost as good with a dielectric constant of 1.001. With this recognition of the low dielectric constant of air, attempts have been made to fabricate semiconductor devices using porous materials as an insulator. Thus, by incorporating air, the dielectric constant of a substance can be lowered.
For example, porosity can be added to silicon dioxide to decrease its effective dielectric constant. Thus, if 50 percent of the volume of a dielectric is air, the effective dielectric constant of the porous silicon dioxide can be calculated by multiplying the percentage of the total volume of the porous dielectric that is air (i.e., 50 percent) times the dielectric of air (1.001 or for ease of calculation 1) and add to it the percentage of the total volume of the porous dielectric that is, for example, silicon dioxide (∈=4). Thus, for s 50/50 mix of silicon dioxide and air the dielectric constant of the porous material is as follows: ∈=0.5*4+0.5*1=2.5. Porous materials, such as the one described above, can be made up with as high as 90 percent air. However, such porous materials suffer from a number of drawbacks, such as, for example, a lack of mechanical and reliability attributes.
Another solution to lowering the dielectric constant of silicon dioxide is to use a spin-on-glass (SOG), which is generally a siloxane based material of low molecular weight, to lower the effective dielectric constant of silicon dioxide. The SOG is heat treated after deposition thereby completing a network of chemical bonds. This creates a xe2x80x9ccage structurexe2x80x9d of SOG and makes the density of the SOG less than that of silicon dioxide. As a result the dielectric constant of the SOG is lower than that of just silicon dioxide. However, such a reduction in the dielectric constant of a substance can be insufficient for some newer electrical applications, for example, high speed integrated circuits.
The present invention provides a method of forming a porous insulating composition comprising the steps of (A) providing at least one organic sacrificial material/dielectric material composition comprising at least one organic sacrificial material and at least one dielectric material; and (B) removing the at least one organic sacrificial material in the at least one organic sacrificial material/dielectric material composition, in order to generate pores in the at least one dielectric material. Additionally, step (B) can comprise heating the at least one organic sacrificial material to a temperature equal to or greater than the decomposition temperature of the at least one organic sacrificial material.
In another embodiment, the present invention provides a method of forming a porous insulating composition comprising the steps of: (A) providing a sacrificial material/dielectric material composition comprising at least one sacrificial material and at least one dielectric material; (B) curing the sacrificial material/dielectric material composition; and (C) thermally decomposing the at least one sacrificial material in the sacrificial material/dielectric material composition, in order to generate pores in the at least one dielectric material.
According to another aspect of the invention, a composition useful in making a porous insulator, comprising a heat-activated, pore-forming, sacrificial material; and a dielectric material is disclosed.
According to still another aspect of the invention, a composition useful in making a porous insulator, comprising at least one pore-forming, organic sacrificial material; and at least one dielectric material, wherein the at least one pore-forming, material is a norbornene-type polymer is disclosed.
Preferably, the organic sacrificial material or sacrificial material is a norbornene-type polymer. Also, the norbornene-type polymer preferably is of the type herein described, which comprises repeating units of the general formula: 
wherein R1 and R4 independently represent hydrogen or linear or branched (C1 to C20) alkyl; R2 and R3 independently represent hydrogen, linear or branched (C1 to C20) alkyl or the groups: 
R9 independently is hydrogen, methyl, or ethyl; R10, R11, and R12 independently represent linear or branched (C1 to C20) alkyl, linear or branched (C1 to C20) alkoxy, linear or branched (C1 to C20) alkyl carbonyloxy, and substituted or unsubstituted (C6 to C20) aryloxy; m is a number from 0 to 4; and n is a number from 0 to 5; and at least one of substituents R2 and R3 is selected from the silyl group represented by the formula set forth under Ia.
More generally, the organic sacrificial materials or sacrificial materials useful in practicing the present invention preferably encompass homopolymers and copolymers containing random repeating units derived from a monomer unit or monomer units represented by Formula I, or homopolymers or copolymers containing random repeating units derived from monomer unit or units represented by the below set forth Formula II, homopolymers or copolymers containing repeating units derived from a monomer unit(s) represented by below set forth Formula III and copolymers comprising a combination of repeating units represented by Formulae I and II, Formulae I and III, Formulae II and III or Formulae I, II and III.
The present invention is advantageous in that it provides a method by which uniformly dispersed pores of relatively the same pore diameter can be created in an insulating material, thereby reducing the dielectric constant of a insulating material.
The foregoing and other features of the invention are hereinafter fully described and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail one or more illustrative embodiments of the invention, such being indicative, however, of but one or a few of the various ways in which the principles of the invention may be employed.